I am not an expert in ProSeries, but I do not believe that it has a "bulk sale feature".  You will either have to do it manually:

https://proconnect.intuit.com/support/en-us/help-article/form-8949/entering-bulk-disposition-assets-...

Or each asset separately.

If you are just asking about allocating the sales, there is no correct answer.  Any reasonable method would be fine.  I think personally, I would just make one manual entry for the sale of all of the assets.

You may want to review the assets with the taxpayer to see if any of them were actually disposed of in prior years.

If I understand you correctly you have $817k of 1245 assets with $763k of depreciation.  It sounds like you will have $346k in profit all subject to depreciation recapture.  I wouldn't use any allocation that gives a different result.